In general, the hydraulic excavator which is a representative example of the construction machine is configured by an automotive lower traveling structure, an upper revolving structure which is revolvably loaded on the lower traveling structure and a working mechanism tiltably provided on the front side of the upper revolving structure and at an intermediate position in a left-right direction.
The upper revolving structure is equipped with a revolving frame which forms a supporting structure member, an engine loaded on the rear side of the revolving frame and a cab provided to be put aside to the left front side of the aforementioned revolving frame which is the left side of the aforementioned working mechanism. An operator's seat on which an operator sits and the like are provided in this cab.
A mounting bracket which is located on the front side and adapted to mount the working mechanism is provided at the intermediate position in the left-right direction of the revolving frame. An oil storage tank such as a fuel tank for storing a fuel, a hydraulic oil tank for storing hydraulic oil or the like is provided on the right side of the revolving frame which is opposite to the cab with the working mechanism interposed. This oil storage tank is arranged such that its front end is located more rearward than the mounting bracket of the revolving frame.
On the other hand, a diesel engine is used as the engine of the hydraulic excavator. This diesel engine is said to emit much nitrogen oxides (hereinafter, referred to as NOx) and the like. Therefore, there exists a NOx purifying device for purifying NOx as a post-processing device for exhaust gas from the diesel engine. This NOx purifying device is configured by a urea selective reduction catalyst provided, for example, in an exhaust pipe of the engine to remove the nitrogen oxides in the exhaust gas, a reducing agent tank for storing a urea water solution as a reducing agent, a urea water injection valve for injecting the urea water solution in the reducing agent tank toward the upstream side of the urea selective reduction catalyst, and connecting piping for connecting together the aforementioned reducing agent tank and the urea water injection valve.
Here, in a case where the reducing agent tank is to be provided on the hydraulic excavator, it is desirable to set the capacity large in order to reduce the water supply frequency. However, since many devices are loaded on the hydraulic excavator, it is difficult to secure a space for newly installing the reducing agent tank. Accordingly, there is known the one configured to accommodate the reducing agent tank in an article accommodating case for accommodating tools and the like in prior art hydraulic excavators (Patent Document 1 and Patent Document 2). Further, as an arrangement place of the reducing agent tank, there is known the one configured to arrange it around the oil storage tank (Patent Document 3).